How to increase the persistence of object id without updating it?


My testing scene has two baby dolls. But if one baby is not seen for several frames (not being recognized), a new id is assigned to him.
How can I change the persistency of keeping the same id? The baby’s clothes and the location are the same, I am surprised the id becomes different…
Btw, tracking is on. I just use the body tracking sample code.

If there is not persistence setting, my plan B is to create my own object id, if the object centre is around the space place, I consider it is the same object.